1. Field of the Invention
This invention relates to a focus detecting apparatus in which a focus detecting region can be changed.
2. Related Background Art
A focus detecting apparatus having a plurality of focus detecting regions in a photographing image field is known (see, for example, Japanese Laid-Open Patent Application No. 63-11906).
In a focus detecting apparatus of this kind, a plurality of focus detecting regions are set in a range corresponding to a photographing image field on a predetermined focal plane, and a plurality of focus detecting optical systems and a plurality of pairs of sensor light receiving portions are provided corresponding to the respective focus detecting regions.
By the focus detecting optical system corresponding to each focus detecting region, a light beam from an object passed through each resion is directed to the pair of sensor light receiving portions corresponding to each region, and on the basis of the output signals of those sensor light receiving portions, the focus adjusted state of a phototaking optical system in each focus detecting region is detected.
However, the above-described focus detecting apparatus suffers from the following problems:
(1) A focus detecting module comprising a plurality of focus detecting optical systems and a plurality of pairs of sensor light receiving portions must be provided correspondingly to a plurality of focus detecting regions and therefore, the cost of the apparatus becomes high.
(2) Since installation space for the large focus detecting module must be secured, the downsizing of the apparatus is difficult.
(3) The plurality of focus detecting regions are fixed in their positional relation with the corresponding focus detecting optical systems and the pairs of sensor light receiving portions and the positions of the focus detecting regions cannot be arbitrarily changed.
(4) It is necessary to dispose the focus detecting regions in suitably spaced apart relationship with one another so that the plurality of focus detecting optical systems and the plurality of pairs of sensor light receiving portions may not interfere with one another, and the focus detecting regions cannot be set at arbitrary positions.
In order to solve such problems, in a focus detecting apparatus disclosed in Japanese Laid-Open Patent Application No. 2-217811, a light beam passed through a phototaking optical system is reflected by a sub-mirror in a camera body and is directed to a focus detecting module provided at the bottom of the camera body and also, the angle of the sub-mirror is varied to thereby change the focus detecting region.
Again in this focus detecting apparatus, however, the above-noted problems are not completely solved, but there are the following problems:
(1) The position and angle, in the direction of the optical axis, of the focus detecting module with respect to a predetermined focal plane deviate due to a change in the angle of the sub-mirror and therefore, focus detection accuracy is reduced.
(2) In the method of changing the angle of the sub-mirror, the focus detecting region can be changed only in the longitudinal direction of the photographing image field.
(3) When the focus detecting region is changed by changing the angle of the sub-mirror, it is necessary to set the angle of the sub-mirror within such a range that the positional relation of the focus detecting module to the predetermined focal plane does not greatly deviate, and the position of the focus detecting region cannot be greatly changed.
Now, it is conceivable to move a focus detecting module itself comprising a focus detecting optical system and a pair of sensor light receiving portions in a plane parallel to a predetermined focal plane to thereby change the focus detecting region.
However, this method would suffer from the following problems:
(1) It is difficult to move the focus detecting module exactly in a plane parallel to the predetermined focal plane and if the position deviates in the direction of the optical axis of a phototaking optical system, the amount of the deviation will provide a focus detection error.
(2) It is necessary to secure a space in which the entire focus detecting module is moved and moreover, a driving mechanism must be provided and thus, the apparatus becomes bulky.
(3) Each time the sensor light receiving portions are moved with the movement of the focus detecting module, stress is applied to a wiring material connected to the sensor light receiving portions and therefore, the connecting portions may come off or the wiring material may be cut.